1. Field of the Invention
The present invention relates to a maximum power point tracking method and a maximum power point tracking device for a solar power system. Particularly, the present invention relates to the maximum power point tracking method actuating a DC/DC converter to perform an active resistance characteristic so as to supply power to a DC/AC inverter or a DC load. More particularly, the present invention relates to the maximum power point tracking method that adjusts the DC/DC converter for changing its active resistance, and monitors a change of output power of a solar cell array.
2. Description of the Related Art
In solar power applications, a most significant subject focused today is associated with a technology of maximum power point tracking in addition to other major technologies which have been developed. Presently, a most common technology for maximum power point tracking is a perturbation and observation method. A conventional perturbation and observation method for maximum power point tracking, described in U.S. Pat. No. 5,327,071, controls a DC/DC converter for tracking a maximum power point of a solar cell array. In maximum power point tracking operation, an output voltage of the solar cell array is initially varied. Secondly, an output power of the solar cell array is subsequently detected. Each new value of the detected output power compares with a previous value in determining a perturbation direction of the output voltage of the solar cell array. In this circumstance, the output voltage of the solar cell array is continuously varied in detecting the maximum power point. Once detected a position of the maximum power point, the output voltage of the solar cell array is continuously varied around this position of the maximum power point for repeatedly re-determining it.
Another conventional perturbation and observation method for maximum power point tracking, described in U.S. Pat. No. 5,932,994, also controls a DC/DC converter so as to further control output voltage of a solar cell array for tracking a maximum power point. In maximum power point tracking operation, a duty cycle of a power switch in the DC/DC converter is initially varied. An output voltage and an output current of the solar cell array are detected to calculate an output power thereof. Each new value of the calculated output power compares with a previous value in determining a direction of fluctuation of the duty cycle of the power switch. In this circumstance, the duty cycle of the power switch is continuously varied in detecting the maximum power point. Once detected a position of the maximum power point, the duty cycle of the power switch is continuously varied around this position of the maximum power point for repeatedly re-determining it.
As has been explained above, these conventional perturbation and observation methods require at least two signals of detected voltages or currents in detecting the maximum power point. However, there exist some problems with practicing these perturbation methods applied to detect the maximum power point. For example, the circuits of maximum power point tracking devices for use in practicing such perturbation and observation methods result in complication of structures, and increase the manufacturing costs. Hence, there is a need for improving these perturbation and observation methods and the maximum power point tracking devices applied thereto.
As is described in greater detail below, the present invention intends to provide a maximum power point tracking method and a maximum power point tracking device for a solar power system. A DC/DC converter connecting with a solar cell array is actuated to perform an active resistance characteristic for supplying power to a DC/AC inverter or a DC load. A maximum power point tracking circuit is further used to adjust the DC/DC converter for changing its active resistance, and to monitor a change of the solar cell array in output power. Accordingly, the maximum power point tracking method and the maximum power point tracking device are simplified, and manufacturing cost thereof is reduced.